1. Field of Invention
The disclosure relates to an antenna module.
2. Related Art
The antennas of conventional mobile phones or tablet computers are usually planar inverted F antennas (PIFA) or monopole antennas. Since the operation bands of conventional communication electronic devices are ranged in low frequency such as from 824 MHz to 960 MHz, the above-mentioned conventional antennas can satisfy the requirements of the narrow bandwidth.
However, due to the rapid development of mobile communication, the latest 4th generation mobile communication specification (4G) has expanded the operation bandwidth at the low frequency to 700 MHz, which is different from the conventional major mobile communication specification (GSM, 960 MHz) by 260 MHz.
In order to increase the additional bandwidth, it is very common to configure another antenna of different operation band for broadening the available bandwidth. However, this method needs to provide a new feeding point as well as another coaxial cable for the additional antenna, which sufficiently increases the dimension of the entire electronic device. In other words, it is very difficult to design the additional antenna in the limited space of the small and compact communication devices.
Other methods for broadening the available bandwidth are to configure the capacitance or inductance matching circuit before the feeding point of the antenna or to weld capacitor or inductor on the antenna. However, these methods can only increase the limited bandwidth. This is because the bandwidth is mainly determined by the radiation impedance of the antenna body. Although the matching circuit configured by the reflective coefficient of the capacitance or inductance slightly improves the bandwidth, this small improvement can not satisfy the requirement for the new generation of mobile communication specification.